Analyzing method and device for automatically sorting products such as fruit

ABSTRACT

A method of analysing products arranges above a conveyer line three successive analysing stations having, in the first station, two cameras arranged in such a way that their optical axes form a V centred on the products and has a vertex angle in the range between 90° and 130°, and in the other two stations, a camera arranged plumb with the conveyer line. Moreover, the products are driven in rotation during their transport along the analysing stations, in such a way that the cameras each take a number of photographs of complementary faces of the surface of the products, and there are selected from among the photographs taken, by a comparison between the calculated theoretical diameter of a product and a predetermined average diameter, the photographs to be retained so as to obtain a complete analysis of the total surface of the product.

BACKGROUND OF THE INVENTION

The invention relates to an analysing method and device with a view tothe automatic sorting of products such as pieces of fruit.

DESCRIPTION OF THE RELATED ART

At the present time, numerous techniques exist which are intended topermit the analysis of products such as pieces of fruit, with a view topermitting the automatic sorting of the products in such a way as toobtain batches which are homogeneous in terms of both quality andcolour.

A first technique consists in arranging one or more cameras above and/oron the side of a conveyer in such a way as to analyse a surface portionof the pieces of fruit transported on the conveyer. However, thissolution leads to a not insignificant error rate, because only oneportion of the surface of the products is analysed. Consequently,defects which these products exhibit on faces which are not visible arenot taken into account during sorting.

In order to overcome this drawback, one solution consists in arrangingfour cameras which are distributed around a conveyer, at its junctionwith another conveyer which is raised in relation to the conveyer, insuch a way as to analyse the pieces of fruit when they drop. Thissolution does, in fact, make it possible to analyse the major part ofthe surface of the products. In the first place, however, this solutiondoes not permit the analysis of the whole of the upper and lower facesof the products. Moreover, the fact that the products are subjected todropping constitutes a not insignificant risk of bruising them.

Another technique which is very commonly employed and which isdescribed, in particular, in U.S. Pat. No. 4,726,898, consists inarranging a camera above the conveyer and in causing the product torevolve on itself at high speed plumb with the camera. According to thistechnique, the position and optical field of the camera are adapted sothat the latter displays four or five pieces of fruit, so that a numberof successive faces of each piece of fruit which is driven in rotationare viewed successively by the camera. One of the advantages derivingfrom this arrangement resides in the fact that a single camera permitsthe analysis of pieces of fruit which are moving along on two parallelconveyer lines. On the other hand, this arrangement makes it necessaryfor the camera to be relatively remote from the conveyer lines, andleads to a loss of resolution which manifests itself in practice in aninability to detect very small specks, such as “diffuse russeting”.Moreover, it turns out that, according to this technique, those speedsof rotation of the pieces of fruit which can be physically obtained leadto the displaying of only about 80% of the total surface of the piecesof fruit. Finally, the defects in those zones of the pieces of fruitwhich are viewed with a high degree of incidence turn out to be poorlyanalysed. The consequence of this combination of facts is that, inpractice, 25% to 30% of the surface of the pieces of fruit is eithersimply not analysed or else is poorly analysed.

In order to overcome this combination of drawbacks, other solutions havebeen proposed which consist, for example, in suspending the products ortransporting them on a transparent conveyer. However, these solutionshave proved unworkable in practice.

Another technique which is described in EP Patent 0,258,810, consists inarranging a camera above the conveyer, a plurality of mirrors which aredistributed above and on the sides of the conveyer in such a way as toallow the camera to display the upper face and side faces of theproducts, and a plurality of lighting lamps distributed above theconveyer. Apart from the lower face of the products, which is resting onthe conveyer, this solution therefore permits the analysis of the majorpart of the surface of the products without the risk of bruising thelatter. However, the implementation of such a technique proves to berelatively complex. In fact, the implementation makes it necessary, inparticular, to arrange the lighting lamps in such a way as not to dazzlethe camera, an arrangement which proves awkward to obtain if it isdesired to obtain uniform lighting. Likewise, the relative positions ofthe camera and the various mirrors have to be absolutely precise, andthis proves to be not very easy because of the congestion problemslinked with the presence of the conveyer. Furthermore, the principleadopted, which consists in using a CCD camera divided up into analyzingsegments, leads to a not insignificant reduction in the resolution ofthe sensor.

Another technique, which is described in Patent Application WO 94/10555and U.S. Pat. No. 5,156,278, consists firstly in providing foursuccessive analysing stations arranged at a distance from one anotheralong the conveyer and each comprising a lens which is arranged plumbwith the conveyer and connected to a lens/filters/photodiodes unit by anoptical cable. Moreover, according to this technique, the pieces offruit are carried by a conveyer equipped with rollers which are mountedso as to rotate freely about a transverse axis, and the rollers arecaused to revolve about their axes of rotation between the stations, sothat each piece of fruit undergoes a rotation of about 90° between twostations, whereas the piece of fruit is rotationally immobile when plumbwith each of the stations. Such a technique therefore makes it possibleto display the whole of the surface of the pieces of fruit owing to thefact that complementary faces of the latter are analysed at eachstation. However, it has one drawback which results from the differencesin size of the pieces of fruit analysed. In actual fact, the rotationwhich a piece of fruit with a given diameter undergoes differs from thatundergone by a fruit with a different diameter so that, since the angleof rotation is necessarily calculated for a piece of fruit with a givenaverage diameter, pieces of fruit which are larger in size are notviewed in their entirety, whereas overlapping zones of pieces of fruitwhich are smaller in size are displayed, leading to erroneous analysisof the surface of the pieces of fruit.

SUMMARY OF THE INVENTION

The present invention sets out to overcome all the drawbacks of thetechniques described above, and has the essential object of providing aproduct-analysing device which is very simple to implement and operateand which permits the analysis of the whole of the surface of theproducts in spite of differences in the dimensions of the latter.

To that end, the invention relates to an analysing method with a view tosorting products such as pieces of fruit which are transported along anaxis (x) on a conveyer line having a plurality of rollers which aremounted so as to each rotate freely about a transverse axis of rotationorthogonal to the axis (x), and which are spaced apart in such a waythat two adjoining rollers define, between them, a seating for aproduct, the analysing method consisting in using analysing means whichare split up into a number of successive stations arranged at a distancefrom one another along the axis (x), and in causing the rollers torevolve about their axes of rotation between the stations in such a wayas to display, at each of the stations, different faces of each product.

In the analysing method according to the invention:

-   -   three analysing stations are arranged along the conveyer line,        and each of the analysing stations is equipped with at least one        camera which is orientated and adapted to make, with an        adjustable frequency, photographs of the products transported by        the conveyer line,    -   one of the stations having two cameras which are arranged on        either side of the conveyer line in the same vertical plane        orthogonal to the axis (x), and are orientated in such a way        that their respective optical axes form a V which is centred on        the axis (x) and has a vertex angle substantially in the range        between 90° and 130°,    -   the other two stations each comprising a camera which is        arranged plumb with the conveyer line and is orientated in such        a way that its optical axis is vertical and secant with the axis        (x),    -   in a preliminary phase, there are determined the average        diameter of the products to be analysed and, as a function of        the average diameter, a speed of rotation of the rollers which        is adapted so that a product of average diameter which is        located in the plane of a camera at the first station and is        caused to revolve on itself along the whole of the analysing        means under the effect of the rotation of the rollers, undergoes        a rotation such that four complementary zones on its surface are        viewed by the respective cameras of the first, second and third        stations,    -   and during the conveying of the products, the rollers are caused        to revolve continuously at the predetermined speed of rotation,        and for each product:    -   mi photographs of this product are made at the first station,        where i≧3, nj photographs at the second station, where j≧1, and        pk photographs at the third station, where k≧3,    -   the theoretical diameter of the product is calculated from the        photographs made,    -   and the photographs mi, nj and pk to be taken into account with        a view to analysing the product are determined by comparison of        the theoretical diameter of this product with the predetermined        average diameter, in such a way as to obtain a complete        analysis, without overlapping or with a given overlap, of the        total surface of the product.

According to the method of the invention, on the one hand the camerasare arranged and orientated, and on the other, each product is caused torevolve continuously during its transport along the analysing device, insuch a way that the product is displayed in accordance with fourdifferent angles adapted to permit the analysis of four complementaryfaces of a product with a given average diameter. Moreover, in order totake into account the differences in diameter of the products analysedin relation to the predetermined average diameter:

-   -   the theoretical diameter of each product is, first of all,        determined in conventional manner,    -   the nature of the photograph to be taken into account with a        view to analysis is deduced, from among the photographs made at        the various stations, from the comparison between the        theoretical diameter calculated and the predefined average        diameter, in such a way as to obtain a complete analysis of the        total surface of the product. This selection of the photographs        to be analysed is carried out very easily. By way of example, if        the photographs mi, nj and pk correspond to a product of average        diameter, and if i, j, k, photographs are taken at each station,        where i−x≦i≦i+x, j−y≦j≦j+y, and k−z≦k≦k+z, the photographs will        be:    -   in the case of a product with a theoretical diameter        substantially equal to the average diameter: mi, nj, pk,    -   in the case of a product with a diameter smaller than the        average diameter, m (i+x), n (j−y) and p (k−z) photographs,        where x, y, z are of an order which is a function of the        difference in diameter,    -   in the case of a product with a diameter greater than the        average diameter, m (i−x), n (j+y) and p (k+z) photographs,        where x, y, z are of an order which is a function of the        difference in diameter.

A method of this kind which therefore combines the use of a number ofcameras distributed and orientated in a specific manner, the setting ofthe products in rotation at a given speed of rotation, and the selectionof the photographs taken by the cameras as a function of the theoreticaldiameter of the products, permits the analysis of the whole of thesurface of each product without overlapping or with a known overlap, andto do so in spite of the differences in size of the products.

According to one advantageous mode of implementation, a speed ofrotation of the rollers is determined which is adapted so that a productof average diameter undergoes a rotation on itself with an angle ofrotation substantially in the range between 110° and 130° between thefirst and second stations, and with an angle of rotation substantiallyin the range between 105° and 115° between the second and thirdstations.

These angles of rotation, which are associated with the arrangement ofthe two cameras situated at one of the stations, lead to the obtentionof shots of each product which are equivalent to those which would beobtained from four cameras arranged at the four vertices of atetrahedron and orientated towards the barycentre of the tetrahedron, byplacing the product at the barycentre.

These angles of rotation may advantageously be obtained:

-   -   by arranging the stations of analysing means in such a way that        the distance between the first and second stations is        substantially in the range between 1.1 and 1.2 times the        distance between the second and third stations,    -   and by causing the rollers to revolve in rotation at a constant        speed of rotation along the whole of the analysing device.

According to one advantageous mode of implementation, a speed ofrotation of the rollers is determined which is adapted so that a productof average diameter undergoes a rotation on itself with an angle ofrotation substantially equal to 125.5° between the first and secondstations, and with an angle of rotation substantially equal to 109°between the second and third stations.

Moreover, the cameras of the station comprising two cameras areadvantageously arranged in such a way that their respective optical axesdefine a V with a vertex angle substantially equal to 109°.

These angles of rotation and orientation of the two cameras lead to theobtention of an optimum shooting system equivalent to a system whosefour cameras would be arranged at the four vertices of a regulartetrahedron.

In order to obtain these angles of rotation, and in an advantageousmanner, the distance between the first and second stations issubstantially equal to 1.15 times the distance between the second andthird stations.

Furthermore, the first station is advantageously equipped with twocameras, and the second and third stations with one camera. The factthat the two cameras are arranged at the first station permits betterdefinition of the theoretical diameter of the products.

Furthermore, and in an advantageous manner, three photographs of eachproduct are taken at the first and third stations, and a singlephotograph of the products at the second station.

The invention extends to an analysing device with a view to theautomatic sorting of products such as pieces of fruit, the devicecomprising:

-   -   a conveyer line for transporting the products along a        longitudinal axis (x), the line having a plurality of rollers        which are mounted so as to each rotate freely about a transverse        axis of rotation orthogonal to the axis (x) and are spaced apart        in such a way that two adjoining rollers define, between them, a        seating for a product,    -   means for analysing the surface of the products, which means are        arranged above the conveyer line and have a number of successive        stations arranged at a distance from one another along the axis        (x),    -   means for driving the rollers in rotation about their axes of        rotation, which means are suitable for bringing about rotation        of the rollers between the analysing stations in such a way that        different faces of the products are analysed at each station,    -   and a processing unit adapted to receive information emanating        from the analysing means, and to calculate workable sorting data        from predefined, programmed criteria.

In the analysing device according to the invention:

-   -   the analysing means comprise three analysing stations, each of        the analysing stations having at least one camera which is        orientated and adapted to make, with an adjustable frequency,        photographs of the products transported by the conveyer line,    -   one of the stations having two cameras which are arranged on        either side of the conveyer line in the same vertical plane        orthogonal to the axis (x), and are orientated in such a way        that their respective optical axes form a V which is centred on        the axis (x) and has a vertex angle substantially in the range        between 90° and 130°,    -   the other two stations each comprising a camera which is        arranged plumb with the conveyer line and is orientated in such        a way that its optical axis is vertical and secant with the axis        (x),    -   the means for driving the rollers in rotation are arranged in        such a way as to bring about continuous rotation of the rollers        along the analysing means, at a speed of rotation which is        adapted so that a product of predetermined average diameter        which is located in the plane of a camera at the first station        and is caused to revolve on itself along the whole of the        analysing means under the effect of the rotation of the rollers,        undergoes a rotation such that four complementary zones of its        surface are viewed by the respective cameras of the first,        second and third stations,    -   the processing unit is adapted to:    -   process, for each product, mi photographs of the products taken        at the first station, where i≧3, nj photographs taken at the        second station, where j≧1, and pk photographs, at the third        station, where k≧3,    -   and to determine, by a comparison of the theoretical diameter of        the product with the predetermined average diameter, the mi, nj        and pk photographs to be taken into account with a view to        analysing the product, in such a way as to obtain a complete        analysis, without overlapping or with a given overlap, of the        total surface of the product.

According to an advantageous mode of embodiment, the first station hastwo cameras, while the second and third stations have a single camera.

Moreover, the distance between the first and second stations isadvantageously substantially in the range between 1.1 and 1.2 times thedistance between the second and third stations. This distance betweenthe first and second stations is preferably substantially equal to 1.15times the distance between the second and third stations.

Moreover, the cameras of the station comprising two cameras areadvantageously orientated in such a way that their respective opticalaxes define a V with a vertex angle substantially equal to 109°.

Furthermore, according to one advantageous mode of embodiment, the meansfor driving the rollers in rotation comprise an endless belt extending,underneath the conveyer line, along the analysing means, and arranged insuch a way as to be tangential to the lower generatrix of the rollers,and means for driving the endless belt which are suitable for causingthe latter to run at a regulable running speed which is different fromthat of the conveyer line.

Moreover, the means for driving the endless belt are advantageouslyadapted to drive it in the same direction of displacement as that of theconveyer line at an adjustable running speed which is lower than that ofthe conveyer line.

Other characteristics, aims and advantages of the invention will emergefrom the detailed description which follows, with reference to theappended drawings which represent, by way of a non-limitative example, apreferred mode of embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a view, in diagrammatic perspective, of an analysing deviceaccording to the invention, installed on a conveyer device having twoproduct-conveying lines,

FIG. 2 is a diagrammatic longitudinal section through a vertical plane Bof the analysing device, and

FIG. 3 is a front view of the analysing device, in the direction of thearrow A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the figures, the analysing device according to the invention isrepresented installed on a fruit-conveying device having two parallelconveying lines 1, 2. Each of these conveying lines 1, 2 comprises aplurality of rollers such as 3, 4 which are mounted so as to each rotatefreely about a transverse axis of rotation, and are spaced apart in sucha way that two successive rollers define, between them, a seating for apiece of fruit. Conveyer lines of this kind are, for example, of thesame type as those described in Patent Application FR-2,772,358, towhich reference may be made for more details.

This analysing device comprises three analysing stations, 5, 6, 7 whichare arranged successively at a distance from one another along theconveyer lines 1, 2, and have, for each of the conveyer lines:

-   -   in the case of the first station 5, two cameras B, 9-10, 11        arranged on either side of the conveyer line 1-2, in the same        vertical plane orthogonal to the direction of displacement of        the conveyer line, the cameras being orientated in such a way        that their optical axes form a V which is centred on a piece of        fruit of average diameter and has a vertex angle substantially        in the range between 90° and 130°,    -   in the case of the second station 6, a camera 12-13 which is        arranged plumb with the conveyer line 1-2, and is orientated in        such a way that its optical axis is vertical and secant in        relation to the longitudinal axis of the conveyer line,    -   in the case of the third station 7, a camera 14-15 which is        arranged plumb with the conveyer line 1-2, and is orientated in        such a way that its optical axis is vertical and secant in        relation to the longitudinal axis of the conveyer line.

Moreover, the analysing stations 5, 6, 7 are spaced apart from oneanother in such a way that the distance 11 between the optical axes ofthe respective cameras 8-11 and 12-13 of the first station 5 and secondstation 6 is equal to 1.15 times the distance 12 between the opticalaxes of the respective cameras 12-13, 14-15 of the second station 6 andthird station 7. In practice, by way of an example, 11 is substantiallyequal to 26 cm, and 12 is therefore substantially equal to 22 cm.

Moreover, the cameras 12-15 of the second station 6 and third station 7are arranged in such a way that their lenses are situated at a height h1which is substantially equal to 80 cm above the conveyer lines, whereasthe lens of the cameras 8-11 of the first station 5 extends to a heighth1-h2, where h2 is substantially equal to 9 cm, above the conveyerlines.

Furthermore, each camera 8-15 has, in a single casing, two distinctcameras such as 16, 17 which are adapted to make photographs which arefully superimposable: a conventional (RVB) camera 16 and an infraredcamera 17. Moreover, these cameras 16, 17 are “single-shot” camerassuitable for taking in the region of 25 photographs per second.

The group of cameras 8-15 is integrated into a single case 18 ofconventional type, which also incorporates lighting means such as 19, ofa type which is known per se.

The analysing device according to the invention further comprises, plumbwith the case 18 and for each conveyer line 1, 2, an endless belt 20,21, which is arranged in such a way as to come into tangential contactwith the lower generatrix of the rollers 3, 4, and means for driving theendless belts, which means are suitable for displacing them at anadjustable speed in the same direction of displacement as that of theconveyer lines.

The functioning of the analysing device according to the invention isdescribed below.

First of all, and in a preliminary phase, the average diameter of thepieces of fruit conveyed is determined. The speed of displacement of theendless belts 20, 21 is then adjusted, as a function of the runningspeed of the conveyer lines 1, 2, in such a way that the rotation of therollers 3, 4 leads an average piece of fruit to undergo a rotation onitself with an angle of 125.50 over the distance 11 separating the firstand second stations 5, 6 and consequently, taking into account theconstant running speed of the endless belts and conveyer lines, arotation on itself of 109° over the distance 12 separating the secondand third stations 6, 7.

In the course of analysis, three mi photographs, where i−1≦i≦i+1, ofeach piece of fruit are taken at the first station 5, a singlephotograph n at the second station, and three pk photographs, wherek−1≦k≦k+1 at the third station.

After conventional, analog/numerical type conversion, these photographsare stored and their processing consists in:

-   -   calculating the theoretical diameter of each piece of fruit from        the mi and n photographs taken at the first and second stations        5, 6,    -   determining, from the calculation of the theoretical diameter,        the photographs to be taken into account with a view to        calculating the workable sorting data, the determination        consisting in selecting:    -   in the case of a piece of fruit with a diameter equal or close        to the average diameter, the mi, n and pk photographs,    -   in the case of a piece of fruit of small size, that is to say        with a diameter smaller than the average diameter, the m (i+1),        n and p (k−1) photographs,    -   and, in the case of a piece of fruit of large size, that is to        say with a diameter greater than the average diameter, the m        (i−1), n and p (k+1) photographs.

It should be noted that although the figures represent a conveyerequipped with two conveyer lines, the analysing device can be installedon a conveyer equipped with n parallel lines, where n≧1, the number ofcameras 815 then being equal to 4 n, with 2 n cameras at the firststation 5, and n cameras at each of the second and third stations 6, 7.

1. An analysing method for sorting products which are transported alongan axis (x) on a conveyer line having a plurality of rollers (3, 4)which are mounted so as to each rotate freely about a transverse axis ofrotation orthogonal to the axis (x), and which are spaced apart in sucha way that two adjoining rollers (3, 4) define, between them, a seatingfor a product, the analysing method consisting in using analysing meanswhich are split up into a number of successive stations (5, 6, 7)arranged at a distance from one another along the axis (x), and incausing the rollers (3, 4) to revolve about their axes of rotationbetween the stations (5, 6, 7) in such a way as to display, at each ofthe stations, different faces of each product, wherein: three analysingstations (5-7) are arranged along the conveyer line, and each of theanalysing stations is equipped with at least one camera (8, 9, 12, 14)which is orientated and adapted to make, with an adjustable frequency,photographs of the products transported by the conveyer line, one of thestations (5) having two cameras (8, 9) which are arranged on either sideof the conveyer line in the same vertical plane orthogonal to the axis(x), and are orientated in such a way that their respective optical axesform a V which is centred on the axis (x) and has a vertex anglesubstantially in the range between 90° and 130°, the other two stations(6, 7) each comprising a camera (12, 14) which is arranged plumb withthe conveyer line and is orientated in such a way that its optical axisis vertical and secant with the axis (x), in a preliminary phase, thereare determined the average diameter of the products to be analysed and,as a function of the average diameter, a speed of rotation of therollers (3, 4) which is adapted so that a product of average diameterwhich is located in the plane of a camera (8, 9) at the first station(5) and is caused to revolve on itself along the whole of the analysingmeans under the effect of the rotation of the rollers, undergoes arotation such that four complementary zones on its surface are viewed bythe respective cameras (B, 9, 12, 14) of the first, second and thirdstations (5-7), and during the conveying of the products, the rollers(3, 4) are caused to revolve continuously at the predetermined speed ofrotation, and for each product: mi photographs of this product are madeat the first station (5), where i≧3, nj photographs at the secondstation (6), where j≧1, and pk photographs at the third station (7),where k≧3, the theoretical diameter of the product is calculated fromthe photographs made, and, from the photographs made at the threestations, the individual photographs from the three stations to be takeninto account with a view to analysing the product are determined bycomparison of the theoretical diameter of the product with thepredetermined average diameter, in such a way as to obtain a completeanalysis, without overlapping or with a given overlap, of the totalsurface of the product.
 2. An analysing method as claimed in claim 1,wherein a speed of rotation of the rollers (3, 4) is determined which isadapted so that a product of average diameter undergoes a rotation onitself with an angle of rotation substantially in the range between 110°and 130° between the first and second stations (5, 6), and with an angleof rotation substantially in the range between 105° and 115° between thesecond and third stations (6, 7).
 3. An analysing method as claimed inclaim 2, wherein the stations (5-7) of analysing means are arranged insuch a way that the distance between the first and second stations (5,6) is substantially in the range between 1.1 and 1.2 times the distancebetween the second and third stations (6, 7), and the rollers (3, 4) arecaused to revolve in rotation at a constant speed of rotation along thewhole of the analysing device.
 4. An analysing method as claimed inclaim 1, wherein a speed of rotation of the rollers (3, 4) is determinedwhich is adapted so that a product of average diameter undergoes arotation on itself with an angle of rotation substantially equal to125.5° between the first and second stations (5, 6), and with an angleof rotation substantially equal to 109° between the second and the thirdstations (6, 7).
 5. An analysing method as claimed in claim 2, whereinthe distance between the first and second stations (5, 6) issubstantially equal to 1.15 times the distance between the second andthird stations (6, 7).
 6. An analysing method as claimed in claim 2,wherein the cameras (8, 9) of the station (5) comprising two cameras arearranged in such a way that their respective optical axes define a Vwith a vertex angle substantially equal to 109°.
 7. An analysing methodas claimed in claim 1, wherein the first station (5) is equipped withtwo cameras (8, 9), and the second and third stations (6, 7) with onecamera (12, 14).
 8. An analysing method as claimed in claim 1, whereinthree photographs of each product are taken by each camera at the firstand third stations (5, 7), and a single photograph of the products istaken by each camera at the second station (6).
 9. An analysing deviceor the automatic sorting of products, the device comprising: a conveyerline for transporting the products along a longitudinal axis (x), theline having a plurality of rollers (3, 4) which are mounted so as toeach rotate freely about a transverse axis of rotation orthogonal to theaxis (x) and are spaced apart in such a way that two adjoining rollers(3, 4) define, between them, a seating for a product, means foranalysing the surface of the products, which means are arranged abovethe conveyer line and have a number of successive stations (5-7)arranged at a distance from one another along the axis (x), means (20)for driving the rollers (3, 4) in rotation about their axes of rotation,which means are suitable for bringing about rotation of the rollersbetween the analysing stations (5-7) in such a way that different facesof the products are analysed at each station, and a processing unitadapted to receive information emanating from the analysing means, andto calculate workable sorting data from predefined, programmed criteria,wherein: the analysing means comprise three analysing stations, each ofthe analysing stations (5-7) having at least one camera (8, 9, 12, 14)which is orientated and adapted to make, with an adjustable frequency,photographs of the products transported by the conveyer line, one of thestations (5) having two cameras (8, 9) which are arranged on either sideof the conveyer line in the same vertical plane orthogonal to the axis(x), and are orientated in such a way that their respective optical axesform a V which is centred on the axis (x) and has a vertex anglesubstantially in the range between 90° and 130°, the other two stations(6, 7) each comprising a camera (12, 14) which is arranged plumb withthe conveyer line and is orientated in such a way that its optical axisis vertical and secant with the axis (x), the means (20) for driving therollers (3, 4) in rotation are arranged in such a way as to bring aboutcontinuous rotation of the rollers along the analysing means, at a speedof rotation which is adapted so that a product of predetermined averagediameter which is located in the plane of a camera (8, 9) at the firststation (5) and is caused to revolve on itself along the whole of theanalysing means under the effect of the rotation of the rollers,undergoes a rotation such that four complementary zones of its surfaceare viewed by the respective cameras (8, 9, 12, 14) of the first, secondand third stations (5-7), the processing unit is adapted to: process,for each product, mi photographs of the products taken at the firststation (5), where i≧3, nj photographs taken at the second station (6),where j≧1, and pk photographs taken at the third station (7), where k≧3,and to determine, by a comparison of the theoretical diameter of thisproduct with the predetermined average diameter, from the photographsmade at the three stations, the individual photographs from the threestations to be taken into account with a view to analysing the product,in such a way as to obtain a complete analysis, without overlapping orwith a given overlap, of the total surface of the product.
 10. Ananalysing device as claimed in claim 9, wherein the first station (5)has two cameras (8, 9), the second and third stations (6, 7) having asingle camera (12, 14).
 11. An analysing device as claimed in claim 9,wherein the distance between the first and second stations (5, 6) issubstantially in the range between 1.1 and 1.2 times the distancebetween the second and third stations (6, 7).
 12. An analysing device asclaimed in claim 11, wherein the distance between the first and secondstations (5, 6) is substantially equal to 1.15 times the distancebetween the second and third stations (6, 7).
 13. An analysing device asclaimed in claim 9, wherein the cameras (8, 9) of the station (5)comprising two cameras are advantageously orientated in such a way thattheir respective optical axes define a V with a vertex anglesubstantially equal to 109°.
 14. An analyzing device as claimed in claim9, wherein the means for driving the rollers (3, 4) in rotation comprisean endless belt (20) extending, underneath the conveyer line, along theanalysing means, and arranged in such a way as to be tangential to thelower generatrix of the rollers, and means for driving the endless beltwhich are suitable for causing the latter to run at a regulable runningspeed which is different from that of the conveyer line.
 15. Ananalysing device as claimed in claim 14, wherein the means for drivingthe endless belt (20) are adapted to drive it in the same direction ofdisplacement as that of the conveyer line at an adjustable running speedwhich is lower than that of the conveyer line.
 16. An analysing methodfor sorting products which are transported along an axis (x) on aconveyer line having a plurality of rollers (3, 4) which are mounted soas to each rotate freely about a transverse axis of rotation orthogonalto the axis (x), and which are spaced apart in such a way that twoadjoining rollers (3, 4) define, between them, a seating for a product,the analysing method consisting in using analysing means which are splitup into a number of successive stations (5, 6, 7) arranged at a distancefrom one another along the axis (x), and in causing the rollers (3, 4)to revolve about their axes of rotation between the stations (5, 6, 7)in such a way as to display, at each of the stations, different faces ofeach product, wherein three analysing stations (5-7) are arranged alongthe conveyer line, and each of the analysing stations is equipped withat least one camera (8, 9, 12, 14) which is orientated and adapted tomake, with an adjustable frequency, photographs of the productstransported by the conveyer line, one of the stations (5) having twocameras (8, 9) which are arranged on either side of the conveyer line inthe same vertical plane orthogonal to the axis (x), and are orientatedin such a way that their respective optical axes form a V which iscentred on the axis (x) and has a vertex angle substantially in therange between 90° and 130°, the other two stations (6, 7) eachcomprising a camera (12, 14) which is arranged plumb with the conveyerline and is orientated in such a way that its optical axis is verticaland secant with the axis (x), in a preliminary phase, there aredetermined the average diameter of the products to be analysed and, as afunction of the average diameter, a speed of rotation of the rollers (3,4) which is adapted so that a product of average diameter which islocated in the plane of a camera (8, 9) at the first station (S) and iscaused to revolve on itself along the whole of the analysing means underthe effect of the rotation of the rollers, undergoes a rotation suchthat four complementary zones on its surface are viewed by therespective cameras (8, 9, 12, 14) of the first, second and thirdstations (5-7), and during the conveying of the products, the rollers(3, 4) are caused to revolve continuously at the predetermined speed ofrotation, and for each product, at least three photographs of thisproduct are made by each camera at the first station (5), at least onephotograph of this product is made by each camera at the second station(6), and at least three photographs of this product are made by eachcamera at the third station (7), the theoretical diameter of thisproduct is calculated from the photographs made, and comparing thetheoretical diameter of this product with the predetermined averagediameter to determine a selection of one of the photographs made at eachof the cameras of the three stations to have a set of selectedphotographs allowing analysis of this product's complete surface withonly a given overlap of surface between any two of the selectedphotographs.
 17. An analysing method as claimed in claim 16, wherein aspeed of rotation of the rollers (3, 4) is determined, which speed ofrotation is adapted so that a product of average diameter undergoes arotation on itself with an angle of rotation substantially in the rangebetween 110° and 130° between the first and second stations (5, 6), andwith an angle of rotation substantially in the range between 105° and115° between the second and third stations (6, 7).
 18. An analysingmethod as claimed in claim 17, wherein the stations (5-7) of analysingmeans are arranged in such a way that the distance between the first andsecond stations (5, 6) is substantially in the range between 1.1 and 1.2times the distance between the second and third stations (6, 7), and therollers (3, 4) are caused to revolve in rotation at a constant speed ofrotation along the whole of the analysing device.
 19. An analysingmethod as claimed in claim 16, wherein a speed of rotation of therollers (3, 4) is determined which is adapted so that a product ofaverage diameter undergoes a rotation on itself with an angle ofrotation substantially equal to 125.5° between the first and secondstations (5, 6), and with an angle of rotation substantially equal to109° between the second and the third stations (6, 7).
 20. An analysingmethod as claimed in claim 17, wherein the distance between the firstand second stations (5, 6) is substantially equal to 1.15 times thedistance between the second and third stations (6, 7).